The instant invention relates to alkene functionalized, metal oxide, nanoparticle composites with polymerizable alkene matrix monomers primarily suitable for dental and medical restoration; i.e., dental restoratives and bone repair, and to the method of their use for such purposes and methods of manufacture. Other applications envisioned include optical elements, X-ray photoresists, and repair of materials.
There have been efforts made to generate functionalized metal oxide nanoparticles to make highly uniform composite materials; namely, in U.S. Pat. No. 5,064,877 by R. Nass et al., in U.S. Pat. No. 5,030,608 by U. Schubert et al.(see also H. Schmidt and H. Wolter, J. Non. Cryst. Solids, 121, 428 (1990). They claim a method for producing functionalized, photopolymerizable particles by replacing groups, R, in M(R).sub.n with groups A which complex M and further contain functional groups which can be photopolymerized. The dispersed, individual metal oxide particles can be prepared by removing R completely, partially replacing by A and then by hydrolyzing to oxide with water. Alternatively, the oxyhydroxide particles may be preformed as M(O).sub.z (OH).sub.x R.sub.y and converted to M(O).sub.z (OH).sub.x A.sub.y by the loss of R. The preformed oxyhydroxide is formed by Nass et al. by the hydrolysis of the organometallic M(R).sub.n by water directly or by water generated by reaction of acid and alcohol unlike Wellinghoff in U.S. Pat. No. 5,570,583 where the oxide is formed by direct ester exchange between a metal alkoxide and a strong organic acid thereby decreasing the number of required reactants.
There have been other attempts to form organic-inorganic hybrid glasses. However, in one case a silane functionalized polymer is hydrolyzed with water to form a network crosslinked by the resultant silica particles making removal of volatile reaction products difficult [Y. Wei et al., Chem. Mater., 2(4), 337 (1990); C. J. T. Landry et al., Polymer, 33(7), 1487 (1992)]. M. Ellsworth et al. [JACS, 113(7), 2756 (1991); U.S. Pat. No. 5,412,043; U.S. Pat. No. 5,254,638] attempted to eliminate the composite shrinkage induced by removal of volatile reaction products by utilizing ring strained alkenoxysilanes and polymerizable solvents where all reaction by products contribute to the SiO.sub.2 network or the resultant interpenetrating, matrix, organic polymer. The expected packing disruption induced by the strained ring opening of the alkenoxysilane was a strategy for compensating for the shrinkage induced by conversion of double bonds to single bonds Zero polymerization shrinkage is one of the most necessary features of a dental restorative so that accumulated stresses do not debond the dentin-restorative interface or fracture the tooth or restorative which can result marginal leakage and microbial attack. This feature is also important in bone repair and in accurate reproduction of photolithographic imprints and optical elements.
Other attempts have been made to reduce polymerization shrinkage by utilizing nematic liquid crystal monomers. The expected low polymerization shrinkage for such compounds originates from the high packing efficiency that already exists in the nematic state, thus minimizing the entropy reduction that occurs during polymerization. Liquid crystal monomers or prepolymers have another advantage in that the viscosity is lower than an isotropic material of the same molecular weight.
M. Aizawa et al. [JP H 5-178794, Jul. 30, 1993] disclose a bisalkene substituted liquid crystal crystal monomer that is suitable for dental restorative materials in combination with silica particle reinforcement. Latter H. Ritter [EP 0,754,675 A2] et al. also disclose liquid crystal monomers that might be suitable for dental applications; however, in neither of the above two patents was the liquid crystal nematic at room temperature or dental temperature. Reactive to diluents were added to the original compounds to generate liquid monomers and it was not clear that liquid crystallinity was present in these mixtures. However, even more recently, J. Klee et al. [WO 97/14674] discuss two liquid crystal monomers that are nematic in the desired temperature range between room temperature and 37.degree. C.
Parent U.S. Application Ser. No. 08/721,742, identified above, discloses bisalkene terminated liquid crystal monomers that form stable liquid crystalline melts between room temperature and 37.degree. C. and their composites with functionalized nanoparticles. This disclosure describes the nanoparticles formed by the reaction of trialkylchlorosilane, formic acid and tantalum alkoxide that are quite acidic in concentrated methanol solution and must be surface functionalized with the base, vinyl imidazole in order to neutralize the excess acidity. The alternative functionalization with an alkene phosphate suffers from the relative hydrolytic instability of the phosphate linkage and the low selectivity of the alkene dimethyl phosphate ester for reactor with Ta--OH bonds. While very satisfactory, the composites are, however, hydrophilic, and this mitigates against their complete suitability for dental purposes.